1. Field of the Invention
The present invention relates to a composite beam formed by a combination between a steel beam and concrete, and more particularly to a steel-concrete composite beam formed by a combination between an asymmetric I-section steel beam and reinforced concrete, in which the asymmetric I-section steel beam is designed so that an upper flange has a narrower than a lower flange.
2. Description of the Prior Art
Generally, a composite beam is integrally formed by a shear connection between a steel beam and a reinforced concrete slab. This composite beam has a bending stiffness about two to three times higher than that of the steel beam alone. Thus, the composite beam has a low deflection resulting from an imposed load, and is particularly advantageous to a beam, which is subjected to a vibration or an impact load.
Further, the composite beam can reduce a weight by 20 to 30% over the reinforced concrete beam, so that it is also advantageous to make a building lightweight. Owing to these advantages, the composite beam is broadly employed at present not only to civil structures such as a bridge and so on, but also to building structures.
However, unlike a civil structure, a building structure is designed to have its section in a way that a neutral axis of the composite beam is usually positioned adjacent to a boundary between a steel beam and a concrete slab. Thus, a compression side flange of the steel beam does not have a great influence on a bending strength. For this reason, the steel beam is manufactured so that its upper flange has a narrower width than that of its lower flange, so that the steel beam has an up-down asymmetrical section. This steel beam is called an xe2x80x9casymmetric section steel beamxe2x80x9d. In this manner, when the steel beam is manufactured to have the asymmetric section, the steel beam can be most effectively reduced in its section without having a great influence on its bending strength. Technique of constructing a floor slab structure using such an asymmetric section steel beam is disclosed in PCT/GB97/00239 (WO 97/30240), which is filed by Peter Wright et al.
Meanwhile, an asymmetric section steel composite beam combining the asymmetric section steel beam with the concrete slab is disclosed in Korean Patent Application Serial No. 2001-4121. Such an asymmetric section steel composite beam is shown in a sectional view in FIG. 1.
As shown in FIG. 1, the conventional asymmetric section steel composite beam includes an asymmetric I-section steel 1 in which an upper flange has a narrower width than an lower flange. Main reinforcing bars 2 are arranged longitudinal to the I-section steel, stirrups 3 enclose the main reinforcing bars. Lower precast concrete 4 is integrated with the lower flange of the I-section steel, and an upper concrete slab 5 integrated with the upper flange of the I-section steel.
This asymmetric section steel composite beam is constructed as follows. In FIG. 2, an asymmetric section steel composite beam prior to formation of the upper concrete slab is shown in a perspective view. First, a beam made up of the I-section steel 1, the main reinforcing bars 2, the stirrups 3 and the lower precast concrete 4 is manufactured at a factory, and then the beam is brought to the construction site and installed between columns or girders. To form the upper concrete slab 5, one end of a metal deck 6 is installed to span each edge of the lower precast concrete 4 as shown in FIG. 2. The upper concrete slab 5 is formed by pouring cast-in-place concrete on the supported metal deck 6 and so forth. As a result, the asymmetric section steel composite beam is completed. Alternatively, the typical form or a half slab may be used in place of the metal deck 6.
In this conventional asymmetric section steel composite beam, the I-section steel 1 is embedded in the upper concrete slab 5 at a predetermined depth. For this reason, when the transverse reinforcing bars of slab are arranged at the lower portion of the upper concrete slab 5, the transverse reinforcing bars of slab cannot be arranged continuously due to interruption caused by the I-section steel 1 embedded in the upper concrete slab 5. Thus, there is a disadvantage in that the transverse reinforcing bars of slab cannot be arranged continuously. Furthermore, this incurs another problem in that the upper concrete slab 5 is partially separated by the I-section steel 1, so that the conventional asymmetric section steel composite beam has weak structural uniformity.
Additionally, in the conventional asymmetric section steel composite beam, in order to unify the lower precast concrete 4 cast at a factory with the upper concrete slab 5 poured on site, the lower precast concrete 4 is provided with the stirrups 3 as shear connectors. In other words, the stirrups 3 are installed to bond between new concrete and old concrete. Installation of these stirrups 3 requires separate reinforcing bars, and thus a construction period becomes extended as well as construction costs become increased, which are considered as other problems.
Further, in order to perform a shear connection between the lower precast concrete 4 and the lower flange of the I-section steel 1, a plurality of studs 7 as shear connectors must be provided on the lower flange of the I-section steel 1.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a steel-concrete composite beam having an asymmetric I-section steel member. The beam has a pair of C-section steel members, thereby having an excellent structural uniformity, eliminating requirement to make use not only of the stirrups for combining the precast concrete with the upper concrete slab, but also of shear connectors such as the studs.
In order to accomplish this object, there is provided a steel-concrete composite beam. The steel-concrete composite beam has an asymmetric I-section steel member having an upper flange, a lower flange and a web. The web is formed with at least one opening at a predetermined interval. The upper flange has a narrower width than the lower flange. A pair of C-section steel members is attached integrally to the lower flange of the asymmetric I-section steel to form a first space. The first space is filled with concrete. The concrete is interlocked with the lower flange. A deck being supported on the C-section steel members and at least one transverse reinforcing bar of slab is arranged through the opening perpendicular to the asymmetric I-section steel member. An upper concrete slab is poured with the concrete to be formed at a predetermined thickness. The concrete is filled in a second space defined by the C-section steel members and the lower flange so that the upper flange of the asymmetric I-section steel is embedded therein.
The above and other objects, advantages and benefits of the present invention will be understood by reference to the detailed description provided below and the accompanying drawings.